mtd: rawnand: sunxi: fix sunxi_nfc_hw_ecc_read_extra_oob

When dumping the OOB, the bytes at the end where actually copied from
the beginning of the OOB instead of current_offset.

That leads to something like:
OOB: ff ff ff ff ff ff ff ff ea 19 00 3a 83 db aa 8d
OOB: 99 09 c8 9a 90 36 35 7d aa 15 13 07 3d 97 b2 a4
OOB: a8 bb 19 b3 07 e9 f6 25 52 d7 1a 23 e2 7e 0a e4
OOB: 52 8a 09 d2 1a 86 3d cf b4 99 43 13 d3 90 33 0b
OOB: ff ff ff ff ff ff ff ff ea 19 00 3a 83 db aa 8d
OOB: 99 09 c8 9a 90 36 35 7d aa 15 13 07 3d 97 b2 a4
OOB: a8 bb 19 b3 07 e9 f6 25 52 d7 1a 23 e2 7e 0a e4
OOB: 52 8a 09 d2 1a 86 3d cf b4 99 43 13 d3 90 33 0b
instead of:
OOB: ff ff ff ff ff ff ff ff ea 19 00 3a 83 db aa 8d
OOB: 99 09 c8 9a 90 36 35 7d aa 15 13 07 3d 97 b2 a4
OOB: a8 bb 19 b3 07 e9 f6 25 52 d7 1a 23 e2 7e 0a e4
OOB: 52 8a 09 d2 1a 86 3d cf b4 99 43 13 d3 90 33 0b
OOB: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
OOB: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
OOB: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
OOB: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
(example with BCH16, user data [8,0], no scrambling)

*cur_off (offset from the beginning of the page) was compared to offset
(offset from the beginning of the OOB), and then, the
nand_change_read_column_op() sets the current position to the beginning
of the OOB instead of OOB+offset

Fixes: 15d6f118285f ("mtd: rawnand: sunxi: Stop supporting ECC_HW_SYNDROME mode")
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Richard Genoud <richard.genoud@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>